There's probably very little in terms of handling between the two (what the 4WD gives the extra weight will no doubt take).
The difference between the two is pretty much just the state of tune. They both map to similar figures with the same hardware
Externally I think the S3 is a nicer, but the Mk5 has a nicer interior and RNS510 is better than RNS-E.
It's swings and round abouts over which you choose really. If you live somewhere snowy I'd get an S3. Otherwise I'd save the money, get an Ed30 and spend the rest on mods.